138,888 research outputs found
On the complexity of curve fitting algorithms
We study a popular algorithm for fitting polynomial curves to scattered data
based on the least squares with gradient weights. We show that sometimes this
algorithm admits a substantial reduction of complexity, and, furthermore, find
precise conditions under which this is possible. It turns out that this is,
indeed, possible when one fits circles but not ellipses or hyperbolas.Comment: 8 pages, no figure
State space description of national economies: the V4 countries
We present a new approach to description of national economies. For this we
use the state space viewpoint, which is used mostly in the theory of dynamical
systems and in the control theory. Gross domestic product, inflation, and
unemployment rates are taken as state variables. We demonstrate that for the
considered period of time the phase trajectory of each of the V4 countries
(Slovak Republic, Czech Republic, Hungary, and Poland) lies approximately in
one plane, so that the economic development of each country can be assocated
with a corresponding plane in the state space. The suggested approach opens a
way to a new set of economic indicators (for example, normal vectors of
national economies, various plane slopes, 2D angles between the planes
corresponding to different economies, etc.).
The tool used for computations is orthogonal regression (alias orthogonal
distance regression, alias total least squares method), and we also give
general arguments for using orthogonal regression instead of the classical
regression based on the least squares method.
A MATLAB routine for fitting 3D data to lines and planes in 3D is provided.Comment: 13 pages, 18 figure
Fast and numerically stable circle fit
We develop a new algorithm for fitting circles that does not have drawbacks
commonly found in existing circle fits. Our fit achieves ultimate accuracy (to
machine precision), avoids divergence, and is numerically stable even when
fitting circles get arbitrary large. Lastly, our algorithm takes less than 10
iterations to converge, on average.Comment: 16 page
Principal arc analysis on direct product manifolds
We propose a new approach to analyze data that naturally lie on manifolds. We
focus on a special class of manifolds, called direct product manifolds, whose
intrinsic dimension could be very high. Our method finds a low-dimensional
representation of the manifold that can be used to find and visualize the
principal modes of variation of the data, as Principal Component Analysis (PCA)
does in linear spaces. The proposed method improves upon earlier manifold
extensions of PCA by more concisely capturing important nonlinear modes. For
the special case of data on a sphere, variation following nongeodesic arcs is
captured in a single mode, compared to the two modes needed by previous
methods. Several computational and statistical challenges are resolved. The
development on spheres forms the basis of principal arc analysis on more
complicated manifolds. The benefits of the method are illustrated by a data
example using medial representations in image analysis.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS370 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Analysis of Deeply Virtual Compton Scattering Data at Jefferson Lab and Proton Tomography
The CLAS and Hall A collaborations at Jefferson Laboratory have recently
released new results for the ep->ep{\gamma} reaction. We analyze these new data
within the Generalized Parton Distribution formalism. Employing a fitter
algorithm introduced and used in earlier works, we are able to extract from
these data new constraints on the kinematical dependence of three Compton Form
Factors. Based on experimental data, we subsequently extract the dependence of
the proton charge radius on the quarks longitudinal momentum fraction.Comment: 25 pages, 26 figure
Detection of a Third Planet in the HD 74156 System Using the Hobby-Eberly Telescope
We report the discovery of a third planetary mass companion to the G0 star HD
74156. High precision radial velocity measurements made with the Hobby-Eberly
Telescope aided the detection of this object. The best fit triple Keplerian
model to all the available velocity data yields an orbital period of 347 days
and minimum mass of 0.4 M_Jup for the new planet. We determine revised orbital
periods of 51.7 and 2477 days, and minimum masses of 1.9 and 8.0 M_Jup
respectively for the previously known planets. Preliminary calculations
indicate that the derived orbits are stable, although all three planets have
significant orbital eccentricities (e = 0.64, 0.43, and 0.25). With our
detection, HD 74156 becomes the eighth normal star known to host three or more
planets. Further study of this system's dynamical characteristics will likely
give important insight to planet formation and evolutionary processes.Comment: 24 pages, 4 tables, 6 figures. Accepted for publication in ApJ. V2
fixed table 4 page overrun. V3 added reference
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